The patellar reflex: does activity of quadriceps femoris muscles reflect leg movement?

The assessment of spinal reflexes has traditionally been performed by clinicians with minimal need for recording equipment, where doctors rely on their training and may use established subjective reflex rating scales. With advances in technology, it is now possible to assess reflexes objectively. This study compared two objective methods of assessing patellar reflex magnitude, duration, and latency, namely electromyography (EMG) of the quadriceps muscles and kinematic assessment of the leg movement around the knee joint.

Reflexes of 24 healthy participants were assessed and seven variables were found to describe each reflex. These were the change in knee angle, the velocity of the reflex, the time to maximum knee angle, the biomechanical movement latency, the EMG maximum amplitude, the negative peak duration, and the EMG latency. Spearman's rank correlation tests were run in order to compare all of the variables.

The results showed that there were positive correlations between EMG maximum amplitude and the change in knee angle (R(2) = 0.75; P < 0.0001) as well as the EMG maximum amplitude and the velocity of the reflex (R(2) = 0.30; P = 0.0058). There was also a negative correlation between EMG maximum amplitude and the biomechanical movement latency (R(2) = 0.35; P = 0.0024).

The results show that there is a relationship between muscle activity and the actual visual movement of the leg assessed using kinematics. This relationship is closest between kinematic measurements and EMG measures of reflex amplitude.